1. Field of the Invention
The present invention pertains to towed-array marine seismic surveying, and, more particularly, to sail line determination in towed-array marine seismic surveying.
2. Description of the Related Art
This section of this document is intended to introduce various aspects of the art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. As the section's title implies, this is a discussion of related art. That such art is related in no way implies that it is also prior art. The related art may or may not be prior art. It should therefore be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
In many areas of the world hydrocarbon reservoirs located in structurally complex areas may not be adequately illuminated even with advanced towed-array acquisition methods. For example, the shallow, structurally complex St. Joseph reservoir off Malaysia produces oil and gas in an area that poses many surveying and imaging challenges. Strong currents, numerous obstructions and infrastructure, combined with difficult near-surface conditions, may hinder conventional survey attempts to image faults, reservoir sands, salt domes, and other geologic features.
To achieve high density surveys in regions having a combination of imaging and logistical challenges, a high trace density and closely spaced streamers may be used. However, this presents the potential of entangling and damaging streamer cables and associated equipment, unless streamer steering devices are closely monitored and controlled. Wide-azimuth towed streamer survey data is typically acquired using multiple vessels, for example: one streamer vessel and two source vessels; two streamer vessels and two source vessels; or one streamer vessel and three source vessels. Many possible marine seismic spreads comprising streamers, streamer vessels, and source vessels may be envisioned for obtaining wide- or rich-azimuth survey data.
Several wide- or rich-azimuth techniques are known to the art. Cole, R. A. et al., “A circular seismic acquisition technique for marine three dimensional surveys”, Offshore Technology Conference, OTC 4864, May 6-9, 1985, Houston, Tex., described a concentric circle shooting scheme for obtaining three dimensional marine survey data around a sub-sea salt dome. Another technique was described by Cole, R. A et al., in the paper presented at the SEG conference in 1988 “Three dimensional marine data acquisition using controlled streamer feathering”, where overlapping circles acquisition is proposed. The concentric circle technique could be useful perhaps when the location of the subsurface feature, like salt dome, is known. The overlapping circles technique could offer an increase in acquisition efficiency versus conventional acquisition.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.